From my understanding, there are 3 types of XP cd's.
1: OEM
2: Retail
3: Volume
OEM and Retail has specific Keys for each CD. The difference between the 2 is that OEM is JUST a CD. No instructions or XP Manual. OEM is typically with big companies like DELL or Gateway. For instance when you buy a Dell computer it will come with a OEM XP cd for that computer.
Retail is if you were to go to staples and grab a XP box.
Volume is issued to business' and any volume key can be used with a volume CD.
Essentially they all contain the same software and settings. Except Home is different than Professional.